The present invention generally relates to a compressor and more particularly, to an electrically driven compressor of the scroll type having a combination of movable and stationary impellers.
FIG. 1 illustrates one of the conventional compressors which is primarily comprised of a closed vessel or housing 101, a compression mechanism portion 102 disposed at the upper portion inside the closed vessel 101, an electric motor 103 disposed under the compression mechanism portion 102 and a lubricating oil sump 104 formed at the bottom portion inside the closed vessel 101. The compressor having the above-described construction is a low pressure type in which a suction pipe 105 is open to the inside of the closed vessel 101 so that pressure on the suction side may be effected therein. An upper vessel 106 is disposed on the discharge side of and above the compression mechanism portion 102 to define a discharge chamber 107 communicating with a discharge pipe 108. As shown by arrows in FIG. 1, refrigerant carrier gas is introduced into the closed vessel 101 from the suction pipe 105 to be compressed at the compression mechanism portion 102 and is discharged into the discharge chamber 107 through a discharge port 109 so that it may flow out towards the side of a refrigeration cycle from the discharge pipe 108.
Such a compressor, however, is subject to some problems, which will be henceforth described, since the compression mechanism portion 102 is disposed inside the closed vessel 101 so as to tightly engage with the inner peripheral surface thereof.
In other words, one of the following means is conceived as a means for securing the compression mechanism portion 102 inside the closed vessel 101:
(1) a press fitting means ensuring the sealing property through a process with high accuracy
(2) a press fitting means ensuring the sealing property by coating a sealing compound or a bonding material
(3) a welding means to be executed from outside.
First, when the means (1) is employed, it is necessary to execute the machining of the engaged portion between the closed vessel 101 and the compression mechanism portion 102 with high accuracy. According, employing this means results in an increased cost and is, therefore, unsuitable for mass production in bulk.
Furthermore, the compression mechanism portion 102 is required to be pressed into the closed vessel 101 by a considerably large pressure in order that the tightness therebetween is ensured by preventing any leak of the pressure between the suction and discharge sides of the compression mechanism portion 102. This press fitting results in an excessive pressure being exerted on the compression mechanism portion 102 and deformation thereof, and consequently, the compression efficiency can not be obtained satisfactorily.
To solve this problem, thickening some parts of the compression mechanism portion 102 to strengthen them has been considered, but such construction does not result in advantageous characteristics associated with weight-saving or a small size.
Secondly, when the means (2) is employed, the sealing compound or bonding material is dissolved by heat produced during the welding between the closed and upper vessels 101 and 106. As a result, the compressor is undesirably reduced in performance, since sufficient air-tightness can not be achieved between the suction and discharge sides of the compression mechanism portion 102.
Thirdly, in case of the means (3), since the compression mechanism portion 102 is primarily made of cast iron, it can be welded to the closed vessel 101 only at a plurality of spaced peripheral portions thereof, but not continuously. Such welding produces deformation between welded portions and non-welded portions, and thus the air-tightness between the suction and discharge sides of the compression mechanism portion 102 can not be satisfactorily ensured.
Moreover, in the compressor having the construction as shown in FIG. 1, a bearing 111 disposed inside the closed vessel 101 has a first surface 111a supporting a thrust bearing 110 and a second surface 111b at which the bearing 111 is kept in contact with a stationary impeller component 112, with the first surface 111a being stepped down from the second surface 111b. Accordingly, the bearing 111 is required to be fitted with high accuracy to ensure sufficient air-tightness between the stationary and rotary impeller components 112 and 113. As a result, the compressor of FIG. 1 is not suited to be produced in bulk.
As described so far, the construction of the compressor shown in FIG. 1 not only inevitably requires high accuracy with regard to design aspects, but when assembling a compressor having such a construction it is difficult to provide the desirable air-tightness in assembling.